1. Field of the Invention
This invention concerns a reaction vessel for carrying out agglutination reactions, and in particular, a reaction vessel used for hemanalysis involving immunological antigen-antibody reactions.
2. Description of the Related Art
Conventional reaction vessels used for detections by using immunological agglutination reactions are, for example, of the type disclosed in U.S. Pat. No. 4,303,616. These reaction vessels are usually referred to by the generic name of microplates.
One detection method using this kind of reaction vessel is particle agglutination method whereby antigens or antibodies in the sample are detected based on an immunological agglutination reaction. In this method, a specific marker particle is used, and antigens or antibodies which conjugate specifically to the substance being measured are coated on the surface of the particle. To detect viruses in blood, for example, a man made marker particle on which the antibodies against for the virus are coated is used. The method is carried out using said reaction vessel as follows. First, said marker particles are mixed with the sample in the reaction vessel, an immunological reaction takes place with the antigens or antibodies in the sample, and the marker particles collect on one of the walls (for example the bottom) of the reaction vessel. The particles collected on the wall of the vessel however have a different distribution pattern depending on whether there was or was not an immunological reaction with the substance being measured in the sample. It is therefore possible to determine a positive or negative reaction for the substance from the distribution pattern of marker particles on the wall of the vessel.
Another method, the mixed agglutination method, was reported by A. S. Wiener and M. H. Herman. This method was subsequently improved in stages so that it could even determine blood group. To determine blood group, for example, the following procedure is carried out using said reaction vessel. First, suitable quantities of a fixed concentration of red blood cells and a fixed dilution of serum are mixed in the reaction vessel, and allowed to stand for a certain time. As in the method described above, the distribution pattern of sedimented red blood cells is different according to whether there was or was not an immunological reaction between antigens on the red blood cells, and antibodies in the serum. It is therefore possible to determine a positive or negative reaction from the distribution pattern of sedimented red blood cells.
In the reaction vessel described in U.S. Pat. No. 4,303,616, however, at least about 50 .mu.l of liquid is required to form a stable and accurate distribution pattern. If the quantity of liquid is less than 50 .mu.l, the sedimentation of particles is disturbed and to be irregular due to surface tension, and the distribution pattern does not form correctly. For this reason, the depth of reaction solution in this reaction vessel requires no less than 3 mm. It is moreover for this reason that the distribution pattern takes a long time to form. In other words, the particles such as red blood cells which form the distribution pattern have to move over a considerable distance, and as a result, the time required to form the pattern is long.
The above problem, namely that the distribution pattern is not formed correctly when the quantity of liquid is too small, can be overcome to some extent by making the internal diameter of the reaction vessel smaller. In this case, however, the surface tension between the reaction solution and the walls of the reaction vessel comes into play, and the liquid surface again sinks or rises irregularly. The result is that it becomes difficult to measure the distribution pattern which is formed accurately.
Further, if the internal diameter of the vessel is made smaller so that the quantity of liquid becomes smaller, the time required to form the distribution pattern is shorter, but the problem then arises that it is necessary to handle minute quantities of reagent. In particular, when the quantity of liquid is no greater than 5 .mu.l, it becomes extremely difficult technically to pipette reagents accurately with high reproducibility.